Although nuclear material accidents are rare, they do occur and safe handling of such accidents must be planned carefully. One of the more critical functions in this area is monitoring of an accident responder""s exposure to airborne radioactivity resuspended in the air at the scene of a nuclear material accident. This is a difficult task, complicated by incomplete characterization of the location and distribution of the contaminants, adverse weather conditions, and accident sites that may be in remote areas.
Typically, air-sampling instruments deployed for assessing airborne radioactivity are classified as either high volume (HiVol) area samplers or personal breathing zone air (BZA) lapel samplers. Both of these types of air-sampling instruments usually require some form of laboratory analysis of their filters at the end of a sampling period, such as a day or a week. Often, analysis may be delayed for a period of time to allow for background decay. Although HiVol filter samples can be checked periodically in the field with hand-held instruments to determine roughly the exposure conditions, the results are approximations, having poor sensitivity.
With these long sampling times and interruptions for background decay, there are significant and dangerous delays in assessing exposure conditions in field locations. As a result, accident responders may be put at risk should the contaminant situation suddenly change due to wind or other factors. In this situation, inadequately protected workers may not be relocated quickly, and engineering and administrative controls may not be used effectively. Alternatively, such conditions could cause workers to be placed into unnecessarily high levels of personal protective equipment (PPE) to assure protection.
As engineering controls may be of limited effectiveness under field conditions, and changes in exposure conditions may develop that are unknown to administrators, heavy reliance often is placed on the use of PPE to assure worker protection. However, the use of PPE has its limits, and associated hazards. For instance, it presents added stress to a worker""s cardiovascular system from the respirator, and heat stress from the protective suit.
These situations can be avoided through use of existing Environmental Continuous Air Monitors (ECAM) having inlets equipped with the present invention. Administrators and managers at the accident site will know about any airborne hazards from frequent (30 or fewer minutes) updates. By combining the radiological and accident meteorological data from an ECAM with the present invention in place and plutonium resuspension forecasting, the conditions likely to be found in the nearby downwind direction also can be brought into administrative and management decisions as they evolve.
U.S. Pat. No. 4,942,774, issued Jul. 24, 1990, to McFarland, for xe2x80x9cAnisokinetic Shrouded Aerosol Sampling Probexe2x80x9d discloses a shrouded probe involving a nozzle having a narrowed diameter end inside a cylindrical shroud. The aerosols captured in the nozzle are input directly into a filter sampler or a continuous air monitor. The present invention differs in significant respects from U.S. Pat. No. 4,942,774, as will hereinafter be made clear.
One of the challenges presented in a field accident location is providing accurate radiation analysis under windy and rainy conditions. The present invention provides a shrouded inlet that smoothes the transition from the ambient wind to the inlet velocity for the ECAM, and that protects the inlet from rain or other precipitation. It further provides particle size selection to exclude large particle components.
It is therefore an object of the present invention to provide a particle size-selected shrouded inlet for an environmental continuous air monitor that smoothes the transition from ambient wind velocity to the proper air velocity for the inlet of the monitor and contemporaneously minimizes the wall losses of aerosol particles in the inlets.
It is another object of the present invention to provide a shrouded inlet that minimizes the entry of rain and other precipitation into the inlet of the continuous air monitor and onto its sample filter.
It is still another object of the present invention to provide a shrouded inlet that removes large particle components in the sampled air by a cyclonic flow of air before such particles reach the sample filter of a continuous air monitor.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects, a wind deceleration and protective shroud for providing representative samples of ambient aerosols to a continuous air monitor (CAM) comprises a cylindrical enclosure having a first end and a second end, the second end being mounted to an input on the continuous air monitor, the cylindrical enclosure defining at least three apertures located radially about its periphery. At least three nozzles having first and second ends, having their first end extending into the cylindrical enclosure through each of the at least three apertures and their second end open to receive ambient air flows direct the air flows upward through said cylindrical enclosure. A sloped platform located inside the cylindrical enclosure supports the first end of the at least three nozzles and causes any moisture entering through the at least three nozzles to drain out through the at least three nozzles; wherein the flow of air creates a cyclonic flow up through the cylindrical enclosure until the flow of air reaches the first end of the cylindrical enclosure and is directed downward to the continuous air monitor.
In another aspect of the present invention and in accordance with its objects and principles, a method of sampling the particulates in a flowing stream of ambient air comprises the steps of decelerating the flowing stream of ambient air; removing a representative sample of particles entrained in the flowing stream of ambient air; creating a cyclonic flow of the representative sample of particles thereby removing any large particle component of the representative sample of particles, leaving a PM-10 inspirable component to be analyzed; and analyzing the PM-10 inspirable component to determine characteristics of any inspirable particulates in the PM-10 inspirable component.